System for simultaneous projections of multiple phase-shifted patterns for the three-dimensional inspection of an object

ABSTRACT

A three-dimensional image grabber allowing for the simultaneous projection of multiple phase-shifted patterns onto an object, and the simultaneous acquisition of multiple images of these phase-shifted patterns is described herein. The grabber comprises a pattern projecting assembly and an image acquisition assembly. The pattern projecting assembly includes, for example, a spectral splitter or a plurality of light sources, grids and projectors for simultaneous projection of a plurality of patterns under different monochromatic lights. The image acquisition assembly includes, for example, a CCD camera sensitive to the different monochromatic lights, or a plurality of CCD cameras with filters to gather lights incoming for the object simultaneously illuminated by the plurality of phase-shifted patterns. A method and a system for measuring the relief of an object, using the above-mentioned process, is also disclosed.

FIELD OF THE INVENTION

The present invention relates to methods for three-dimensionalinspection objects. More specifically, the present invention isconcerned with a system for simultaneous projections of multiplephase-shifted patterns onto objects for their three-dimensionalinspection.

BACKGROUND OF THE INVENTION

The use of interferometric methods for three-dimensional inspection ofan object or to measure the variations of height (relief) of an objectis well known. Generally stated, these methods consist in generating aninterferometric pattern on the surface of the object and then analyzingthe resulting interferometric image (or interferogram) to obtain therelief of the object. The interferometric image generally includes aseries of black and white fringes.

Interferometric methods that require the use of a laser to generate theinterferometric pattern are usually called “classic interferometricmethods”. In such classic methods, the wavelength of the laser and theconfiguration of the measuring assembly generally determine the periodof the resulting interferogram. Classic interferometry methods aregenerally used in the visible spectrum to measure height variations inthe order of micron.

However, there has been difficulty in using such a method to measureheight variations on a surface showing variations in the order of 0.5-1mm when they are implemented in the visible spectrum. Indeed, thedensity of the black and white fringes of the resulting interferogramincreases, causing the analyzis to be tedious.

Another drawback of classic interferometric methods is that they requiremeasuring assemblies that are particularly sensitive to noise andvibrations.

Three-dimensional inspection methods based on Moiré interferometry allowfor a more accurate measurement of the object in the visible spectrum ascompared to the accuracy of classic interferometric methods. Thesemethods are based on the analyzis of the frequency beats obtainedbetween 1) a grid positioned over the object to be measured and itsshadow on the object (“Shadow Moiré Techniques”) or 2) the projection ofa grid on the object, with another grid positioned between the object,and the camera that is used to photograph the resulting interferogram(“Projected Moiré Techniques”). In both cases, the frequency beatsbetween the two grids produce the fringes of the resultinginterferogram.

More specifically, the Shadow Moiré technique includes the steps ofpositioning a grid near the object to be measured, providingillumination from a first angle from the plane of the object (forexample 45 degrees) and using a camera, positioned at a second angle(for example 90 degrees from the plane of the object), to photograph theinterferogram.

Since the distance between the grid and the object varies, thisvariation of height produces a variation in the pattern of theinterferogram. This variation in the pattern can then be analyzed toobtain the relief of the object.

A drawback to the use of a Shadow Moiré technique for measuring therelief of an object is that the grid must be very closely positioned tothe object in order to yield accurate results, causing restrictions inthe set-up of the measuring assembly.

The Projected Moiré technique is similar to the Shadow Moiré techniquesince the grid, positioned between the camera and the object, has afunction similar to the shadow of the grid in the Shadow Moirétechnique. However, a further drawback of the Projected Moiré techniqueis that it involves many adjustments, and therefore generally producesinaccurate results since it requires the positioning and tracking of twogrids. Furthermore, the second grid tends to obscure the camera,preventing it from being used simultaneously to take other measurements.

The use of methods based on “phase-shifting” interferometry allowsmeasurement of the relief of an object by analyzing the phase variationsof a plurality of images of the object after projections of a patternthereto. Each image corresponds to a variation of the position of thegrid, or of any other means producing the pattern, relative to theobject.

Indeed, the intensity I(x,y) for every pixel (x,y) on an interferometricimage may be described by the following equation:I(x,y)=A(x,y)+B(x,y)·cos (ΔΦ(x,y))  (1)where ΔΦ is the phase variation (or phase modulation), and A and B are acoefficient that can be computed for every pixel.

In the PCT application No. WO 01/06210, entitled “Method And System ForMeasuring The Relief Of An Object”, Coulombe et al. describe a methodand a system for measuring the height of an object using at least threeinterferometric images. Indeed, since Equation 1 comprises threeunknowns, that is A, B and ΔΦ, three intensity values I₁, I₂ and I₃ foreach pixel, therefore three images are required to compute the phasevariation ΔΦ.

Knowing the phase variation ΔΦ, the object height distribution (therelief) at every point h(x,y) relative to a reference surface can becomputed using the following equation (see FIG. 1):

$\begin{matrix}{{h( {x,y} )} = {\frac{{{\Delta\Phi}( {x,y} )} \cdot p}{2{\pi \cdot {\tan(\theta)}}}30}} & (2)\end{matrix}$where p is the grid pitch and θ is the projection angle, as describedhereinabove.

The three images used by Coulombe et al. correspond to small translationof a grid relative to the surface of the object. The displacements ofthe grid are so chosen as to yield phase variations in the images.Coulombe et al. suggest obtention of the images by using a system thatallows moving the grid relative to the object to be measured. A minordrawback of such a system is that it requires moving the grid betweeneach take of images, increasing the image acquisition time. This can beparticularly detrimental, for example, when such a system is used toinspect moving objects on a production line. More generally, any movingparts in such systems increase the possibility of imprecision and alsoof breakage.

A method and a system for three-dimensional inspection of an object freeof the above-mentioned drawbacks of the prior-art is thus desirable.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there isprovided a three-dimensional image grabber comprising:

a pattern projecting assembly for simultaneously projecting at least twophase-shifted patterns onto an object; each of the projected patternsbeing characterized by a predetermined bandwidth; and

an image acquisition apparatus sensitive to the predetermined bandwidthsfor simultaneously taking an image of each of the projected patterns onthe object.

According to another aspect of the present invention, there is provideda system for measuring the relief of an object, the system comprising:

a pattern projecting assembly for simultaneously projecting at leastthree phase-shifted patterns onto the object; each of the projectedpatterns being characterized by a predetermined bandwidth;

an image acquisition apparatus sensitive to the predetermined bandwidthsfor taking an image of each of the at least three phase-shiftedprojected patterns on the object; each of the images including aplurality of pixels having intensity values; and

a controller configured for:

-   -   a) receiving from the image acquisition apparatus the at least        three images of the projected patterns onto the object;    -   b) computing the object phase for each pixel using the at least        three object intensity values for the corresponding pixel; and    -   c) computing the relief of the object at each pixel position        using the object phase at the corresponding pixel position.

A system according to the present invention may advantageously be usedfor lead-coplanarity inspection.

According to still another aspect of the present invention, there isprovided a method for measuring the relief of an object comprising:

simultaneously projecting at least three phase-shifted patterns onto theobject;

-   -   a) taking an image of each of the at least three phase shifted        patterns on the object to gather an intensity value at pixel        positions on the image;    -   b) computing the object phase for each of the pixel positions        using the at least three object intensity values for the        corresponding pixel; and    -   c) computing the relief of the object at each pixel position        using the object phase at the corresponding pixel position.

A system and a method for measuring the relief of an object according toembodiments of the present invention are advantageous since they allowsinspection of a moving object using fixed components.

Other objects, advantages and features of the present invention willbecome more apparent upon reading the following non-restrictivedescription of preferred embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a schematic view illustrating the projection of a grid on anobject;

FIG. 2 is a schematic view of a system for measuring the relief of anobject according to an embodiment of the present invention;

FIG. 3 is a schematic view of the three-dimensional image grabber ofFIG. 2 according to a first embodiment of the present invention;

FIG. 4 is a schematic view of a spectral splitter according to anembodiment of the invention;

FIG. 5 is a schematic view of the three-dimensional image grabber ofFIG. 2 according to a second embodiment of the present invention;

FIG. 6 is a schematic view of the three-dimensional image grabber ofFIG. 2 according to a third embodiment of the present invention;

FIG. 7 is a schematic view of the three-dimensional image grabber ofFIG. 2 according to a fourth embodiment of the present invention; and

FIG. 8 is a block diagram m illustrating a method for measuring therelief of an object according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIGS. 2 and 3 of the appended drawings, a system 10 formeasuring the relief of an object, according to an embodiment of thepresent invention, will be described.

The system for measuring the relief of an object 10 comprises a gridprojecting assembly 11, an image acquisition apparatus 12, and acontroller in the form of computer 14 advantageously provided with astoring device 16, an output device 18 and an input device 20. Together,the grid projecting assembly 11 and the image acquisition apparatus 12form a three-dimensional image grabber (hereinafter referred to as a “3Dgrabber”) 15 and will be described hereinbelow in more detail.

The computer 14 is advantageously configured to process the imagesobtained by the system 15 and to analyze these images to measure therelief of an object 30 (see, for example, FIG. 3).

The image processing and the measurement of the relief of the object 30may be advantageously done using a method according to an embodiment ofthe present invention, as will be described further. However, othermethods can also be used, without departing from the spirit and natureof the three-dimensional image grabber of the present invention.

The computer 14 is advantageously provided with memory means allowingthe storage of the images when they are processed by the computer 14 totherefore increase the processing speed.

The storing device 16 can be, for example, a hard drive, a writableCD-ROM drive or other well-known data storing means. It can be directlyconnected to the computer 14, or remotely connected via a computernetwork such as the Internet. According to an embodiment of theinvention, the storing device 16 is used to store both the images takenby the image acquisition apparatus 12, the relief of the object 30 andother intermediary results. Those files can be stored in many format andresolution that can be read by the computer 14.

The output device 20 allows visualization of the images and of the dataproduced by the computer 14, and can take many forms from a displaymonitor to a printing device.

The input device 18 can be a conventional mouse, a keyboard or any otherwell-known input device, or combination thereof, which allows inputtingof data and commands into the computer 14.

The computer 14 can be a conventional personal computer or any otherdata processing machine that includes a processor, a memory andinput/output ports (not shown). The input/output ports may includenetwork connectivity to transfer the images to and from the storingdevice 16.

Of course, the computer 12 runs software that embodies a method formeasuring the relief of an object, as will be described hereinbelow.

Turning now specifically to FIG. 3 of the appended drawings, a 3Dgrabber 15, according to a first embodiment of the present invention,will be described in more detail.

The grid projection assembly 11 includes an illuminating assembly 22, agrid 24 mounted to a support (not shown), and a projector 28.

The illuminating assembly 22 advantageously includes a source of whitelight 34 that is projected through the grid 24. For example, the source34 is the end of an optical fiber (not shown) providing light from awhite light source (not shown). An aspherical lens 36 or any othercondenser is also advantageously used between the source 34 and the grid24. It is believed to be within the reach of a person skilled in the artto conceive another illuminating assembly within the spirit of thepresent invention. Alternatively, the grid may be replaced by anypattern mounted in a frame.

According to a first embodiment of the present invention, theilluminating assembly 22 also includes a spectral splitter (or “lightsplitter”) 35 positioned between the illuminating assembly 22 and thegrid 24 (see FIG. 4). The spectral splitter 35 is designed to decomposethe white light 37 produced by the light source 34 into at least twodifferent monochromatic lights (each of the three styles dashed lines inFIG. 4 represent a monochromatic light) or two non overlappingbandwidths.

Of course, if one of the 3D image grabbers 15, 17, 19 and 21 is to beused for the measure of the relief of an object using a phase-shiftedmethod, they should be modified to simultaneously project at least threephase-shifted grids as will be explained hereinabove.

Alternatively, any means configured to decompose white light into aplurality of monochromatic lights or into two non overlapping bandwidthsmay also be used.

Also, a non-white source of light including a plurality of monochromaticlight may alternatively replace the source of white light.

Since devices producing such results are believed to be well-known inthe art, they will not be described herein in further detail.

The configuration of the grid 24 may vary depending on the resolutionthat is required to adequately measure the relief of the object 30. Forexample, it has been found that a ronchi ruling having 250 lines perinch allows measurement of the lead coplanarity of a circuit board,where a resolution of approximately 1 mm is required.

A projector 28, in the form of a 50 mm TV lens, is advantageously usedto project the grid 24 onto the object 38.

The use of a white light source 34 projected through a spectral splitter35 and then through a grid 24 advantageously allows the simultaneousprojection of at least two monochromatic phase-shifted grids onto theobject 30.

The spectral splitter 35 may alternatively be in the form of aprism-like device, decomposing the white light into a continuousspectrum of light. In the current example, the image acquisitionapparatus 12 may be configured to be sensitive to a discrete number ofwavelengths.

The angle θ between the direction of incidence of the light (dashed line42 on FIG. 2) and the line of sight of the image acquisition apparatus12 (dashed line 44 on FIG. 2) may vary depending on the nature of theobject 30 to be measured.

It is believed to be within the reach of a person skilled in the art toposition the illuminating assembly 22, the grid 24 and the gridprojector 28 relative to the object 30, to yield projected grids havingthe desired pitch p onto the object 30.

For example, a ronchi grid, having a density of 250 lines per inch, witha distance 43 of 22 cm between the object 30 and the projector 28, andfor an angle θ of 30 degrees, provides projected grids having a 0.5 mmpitch p. Such a pitch is equivalent to a variation of height of about 1mm on the surface of the object 30.

Obviously, the pitch of the projected grids will vary with the pitch ofthe grid 24.

It is to be noted that the system 10 does not require a grid between thecamera 46 and the object 30. This advantage will be discussedhereinbelow.

Alternatively, the grid projection assembly 11 may be configured toproject any other pattern by substituting the grid 24 for asemi-transparent plate including a characterized design.

The image acquisition apparatus 12 includes a camera 46 provided with anarray of pixels, which is advantageously in the form of a color CCDcamera, configured to be sensitive to the wavelengths of the projectedgrids. Each of these cameras provide, for example, a resolution of1300×1024 pixels.

The image acquisition apparatus 12 may include a telecentric lens 48,advantageously mounted to the camera 46 via an optional extension tube50.

The configuration of the image acquisition apparatus 12 and the distancebetween the apparatus 12 and the object 30 determines the field of viewof the image acquisition apparatus 12. Alternatively, a desired field ofview can be achieved without the extension tube 50 by adequatelydistancing the camera 46 from the object 30.

An image acquisition apparatus 12 allows to simultaneously take aplurality of images of phase-shifted projected grids onto the object 30.

It is to be noted that the system 10 includes an adjustable supportmeans (not shown) to position the image acquisition apparatus 12 and thegrid projecting assembly 11 relative to each other and to the object 30.Alternatively, other registration means can be used without departingfrom the nature and spirit of the present invention.

Turning now to FIG. 5, a second embodiment of 3D grabber 17 will now bedescribed. Since the only differences between the second and firstembodiments are in the image acquisition assembly, and for concisionpurposes, only those differences will be described herein in furtherdetail.

The image acquisition apparatus 12′ includes three cameras 46, each inthe form of a CCD camera.

The use of semi-transparent mirrors and filters 52-56 allow redirectionof light coming from the object 30 at an angle θ to one of the three CCDcameras 46. The filters allow discrimination of the wavelengthscorresponding to the three projected grids.

More particularly, a first semi-transparent mirror 52 is configured toreflect the first wavelength intended onto a first camera 46 and toallow the remainder of the light to pass through it, including thesecond and third wavelengths. The second wavelength is reflected onto asecond camera 46 by the second semi-transparent mirror 54 that is chosenso as to let the third wavelength through it. The third mirror 56 thenreflects the light having the third wavelength onto a third camera 46.

Each of the three CCD cameras 46 advantageously includes a filter thatallows obtention of the above-described result.

It is to be noted that, in both image acquisition apparatus 12 and 12′,the CCD cameras can alternatively be replaced by CMOS (ComplementaryMetal-Oxide-Silicon) devices.

Although, the image acquisition apparatuses 12 and 12′ have beendescribed so configured as to discriminate monochromatic light, it isbelieved to be within the reach of a person skilled in the art to modifythese apparatuses to discriminate lights having predetermined bandwidth.

Turning now to FIG. 6, a third embodiment of a system 19 for obtainingphase-shifted images will now be described. Since the only differencesbetween the third and second embodiments are in the projecting assembly,and for concision purposes, only those differences will be describedherein in further detail.

The projecting assembly 11′ includes three grid projecting apparatus,each comprising a source with a grid 24 and a projector 28 similar tothe grouping of FIG. 3 or 5, with the difference that the light source34′, 34″ and 34′″ are not sources of white light but emit a light beamhaving a predetermined wavelength different from one another.

Each of the produced beams of light are directed along a direction ofincidence (dashed lines 42′, 42″ or 42′″) and are redirected along theincidence path 42 using a reflecting arrangement that includes mirrors58 and 62 and semi-transparent mirrors 60 and 64. Since such anarrangement of mirrors is believed to be within the reach of a personskilled in the art, it will not be described herein in further detail.

To preserve a constant pitch p for each of the projected grids, thelongitudinal distance from the object of each pattern projectingapparatus may vary. Alternatively, when such constant pitch p is notpreserved, the difference in path of the incidence rays must be takeninto account when using the resulting images for computing the relief ofan object.

Obviously, the projecting assembly 11′ and the image acquisitionassembly 12 may be combined in a fourth embodiment of a 3D grabber 21according to the present invention (see FIG. 7). Again, as in the caseof the first three embodiments described hereinabove, the system 21allows the simultaneous projection of three phase-shifted patterns ontoan object and to then simultaneously take images of these projectedpatterns.

Although the systems 15, 17, 19 and 21 have been described as beingconfigured to simultaneously project three patterns, a 3D grabberaccording to the present invention can be configured and used tosimultaneously project any number of patterns more than two.

It is to be noted that even though three pattern projecting apparatusare illustrated in FIGS. 6 and 7, it is believed to be within the reachof a person skilled in the art to modify the 3D grabber of the presentinvention to allow the simultaneous projection of any number of patternsmore then two.

Turning now to FIG. 8 of the appended drawings, a method for measuringthe relief of an object, according to an embodiment of the presentinvention, will be described in further detail.

Generally stated, the method consists in measuring the relief of anobject 30 by performing the following steps:

100—simultaneously projecting at least three phase-shifted grids ontothe reference object;

102—simultaneously taking an image of each of the phase-shifted grids onthe reference object to gather an intensity value for each pixel of theimages;

104—computing the phase for each pixel of the reference images using theintensity values;

106—repeating steps 100 to 104 by replacing the reference object withthe object 30 to be measured;

108—computing, for each pixel, the difference of height between theobject 30 and the reference object by using the respecting phasesthereof for every pixel; and

110—determining the relief of the object for each pixel using thedifference of height at every pixel.

These general steps will now be further described with reference to afirst example where the object to be measured is a lead sphere mountedto a board. However, it is to be noted that a method for measuring therelief of an object according to an embodiment of the present inventionallows measurement of the relief of other three-dimensional objects.

By choosing a plain board as the reference object, the difference ofheight between the object and the reference object will provide theheight of the sphere. The common element to the object 62 and thereference object is, in this example, the board.

In step 100, the system 10 is used to simultaneously project threephase-shifted grids onto the plain board. As it has been discussedhereinabove, the system 10 includes a means to register and fix theposition of the grid(s) 24 and the camera(s) 46 relative to thereference object (and later the object).

The system 10 is also used to simultaneously take one image of the threephase-shifted grids on the reference object (step 102).

Each image includes an intensity value for each pixel of the image. Thecomputer 14 stores these intensity values for future processing.

It is to be noted that the minimum number of phase-shifted imagesobtained by the system 10 is three, since Equation 1 comprises threeunknowns, that is A, B and ΔΦ, and therefore three intensity values I₁,I₂ and I₃ for each pixel are required to compute the phase variation ΔΦ.

The system 10, and more specifically the 3D grabber 15 (or 17 or 19 or21), allows obtention of images of a projected phase-shifted grid ontoan object similar to images that could have been successively obtainedby translating the grid 24 between each take.

This results in three equations similar to Equation 1 for each pixel ofthe pixel array of the camera 46:I _(n) =A+B ·cos (ΔΦ+Δφ_(n))  (2)

where n=1,3.

By solving the system of Equation 2, one obtains the value of ΔΦ. Thewavelengths of the three projected grids are chosen so as toadvantageously provide different values of Δφ₁,Δφ₂, and Δφ₃.

In step 104, the phase is computed using the three intensity values foreach pixel by solving the Equations 2. This can be achieved by using aconventional numerical method, for example. Numerical methods forsolving such system of equation are believed to be well known in the artand will not be described herein.

Since the method of FIG. 8 requires at least three images to measure therelief of an object, providing more than three images allows to selectthe three best values for computing the phase among the four availablevalues for every pixels. Indeed, most methods for computing the reliefof an object requires four values and do not provide the opportunity toselect the best value when four images are available and one of these issaturated or noisy.

When the method of FIG. 8 is used to inspect a series of objects, steps100 to 104 may be advantageously performed only once for the referenceobject before the inspection. This allows the speed of the inspection tobe increased.

Images of the reference object that would have been obtained prior toany measurement of the object may also be provided.

Steps 100 to 104 are repeated by replacing the reference object with theobject to be measured (step 106).

Since there is no difference in performing steps 100 to 104 with theobject and with the reference object, and for concision purposes, thesesteps will not be described again by referring to the object.

Other methods of computing the phase of the object and/or of thereference object may alternatively be used without departing from thespirit of the present invention. These alternative methods are believedto be well-known in the art and will therefore not be described hereinin further detail.

In step 108, the difference of height between the object 30 and thereference object is computed for every pixel, as obtained in step 104,by subtracting the phase of the reference object from the phase of theinspected object.

It is to be noted that the phases computed in step 104 for the objectand for the reference object correspond to surface phases relative to animaginary projection plan.

When a non-parallel projection of the grid(s) 24 is done, this imaginaryprojection plan becomes slightly curved. This is not detrimental to themethod for measuring the relief of an object, according to the presentinvention, since both the images of the object and of the referenceobject are taken with the same system 10.

Since the phases of the object and of the reference object at each pixelcorrespond to the difference of height between the object (or thereference object) and the same imaginary projection plane (since thesame system with the same optical set-up is used), their subtractionyields the difference of height between the object and the referenceobject. This allows the image acquisition of the object and of thereference object to be performed under different illumination.

In the optional step 110, the relief of the object, i.e. its height, isdetermined for each pixel, using the difference of height at every pixelbetween the object and the reference object, and knowing the dimensionsof the reference object.

As will now appear obvious to a person of ordinary skills in the art, amethod according to an embodiment of the present invention can be usedto measure the difference of height between two objects (one being thereference). In this case, step 110 is obviously not performed.

In some applications, it may be advantageous to use a plane surface onwhich the object to measure will be laid on during measurement as thereference object.

In some applications, it may be advantageous to provide the system 10with a registration system to help position the object and the referenceobject to a known position relative to the camera(s). Indeed, since acomparison between the object and the reference object is performed foreach pixel, a registration system may ensure that corresponding pointsare compared.

Such registration system may take many forms including indicia on planesurface, a stand or a software program implemented in the computer.

It is to be noted that the images may be acquired first and may beprocessed at a future date without departing from the spirit of thepresent invention.

As will be apparent on reading the present description, a method,according to an embodiment of the present invention, allows measurementof the relief of an object using white light.

Although the present invention has been described in an example in whichspherical objects are measured, it allows for the inspection andmeasurement of objects having other configurations.

The same object may also act as the reference object when the system 10is used to study the variation in time of an object's relief.

Alternatively, the reference object may be replaced by a computer modelof the object, generated, for example, by a Computer Assisted Design(CAD) that would have been virtually positioned according to the set-upof the system 10.

Although the present invention has been described hereinabove by way ofpreferred embodiments thereof, it can be modified without departing fromthe spirit and nature of the subject invention, as defined in theappended claims.

1. A three-dimensional image grabber comprising: a pattern projectingassembly for simultaneously projecting at least two phase-shiftedpatterns onto an object; each of said projected patterns beingcharacterized by a predetermined bandwidth; said pattern projectionassembly including a semi-transparent plate including a pattern to beilluminated by an illuminating assembly, a spectral splitter to bepositioned between said plate and said illuminating assembly and aprojector for projecting said illuminated plate onto said object; saidilluminating assembly including a source of white light so positioned asto be projected through said plate; and an image acquisition apparatussensitive to said predetermined bandwidths for simultaneously taking animage of each of said projected patterns on the object.
 2. Athree-dimensional image grabber as recited in claim 1, wherein at leastone of said predetermined bandwidth includes a single wavelength.
 3. Athree-dimensional image grabber as recited in claim 1, wherein saidilluminating assembly further includes an optical fiber and a condenserfor bringing light from said white source to said plate.
 4. Athree-dimensional image grabber as recited in claim 1, wherein saidsemi-transparent plate is a grid.
 5. A three-dimensional image grabberas recited in claim 1, wherein said pattern projection assembly includesat least two pattern projecting apparatuses and a reflectingarrangement; each of said pattern projecting apparatus being configuredto project a light having a predetermined bandwidth through a pattern;said reflecting arrangement being so configured as to direct saidprojected patterns along a common direction of incidence.
 6. Athree-dimensional image grabber as recited in claim 5, wherein at leastone of said pattern projecting apparatuses includes a semi-transparentplate including a pattern to be illuminated by an illuminating assemblyand a projected for projecting said illuminated plate onto saidreflecting arrangement; said illuminating assembly including a source oflight having a predetermined bandwidth and being so positioned as to beprojected through said plate.
 7. A three-dimensional image grabber asrecited in claim 5, wherein said projecting arrangement includes atleast one of said a mirror and a semi-transparent mirror.
 8. Athree-dimensional image grabber as recited in claim 5, wherein saidplate is a grid.
 9. A three-dimensional image grabber as recited inclaim 5, wherein said pattern projecting apparatuses are so positionedrelative to each other as to each provide the same distance from saidrespective plate to the object.
 10. A three-dimensional image grabber asrecited in claim 1, wherein said image acquisition apparatus includes atleast one camera sensitive to said predetermined bandwidth.
 11. Athree-dimensional image grabber as recited in claim 10, wherein saidimage acquisition apparatus includes a telecentric lens.
 12. Athree-dimensional image grabber as recited in claim 1, wherein saidimage acquisition apparatus includes at least two cameras, eachsensitive to one of said predetermined bandwidth.
 13. Athree-dimensional image grabber as recited in claim 10, wherein saidcamera is selected from the group consisting of a Charge Coupled Device(CCD) camera and a Complementary Metal-Oxide-Silicon (CMOS) device. 14.A system for measuring the relief of an object, said system comprising:a pattern projecting assembly for simultaneously projecting at leastthree phase-shifted patterns onto the object; each of said projectedpatterns being characterized by a predetermined bandwidth; an imageacquisition apparatus sensitive to said predetermined bandwidths fortaking an image of each of said at least three phase-shifted projectedpatterns on the object; each of said images including a plurality ofpixels having intensity values; and a controller configured for: a)receiving from the image acquisition apparatus said at least threeimages of the projected patterns onto the object; b) computing theobject phase for each pixel using the at least three object intensityvalues for the corresponding pixel; and c) computing the relief of theobject at each pixel position using said object phase at thecorresponding pixel position.
 15. A system as recited in claim 14,wherein said image acquisition apparatus includes at least one camerasensitive to said predetermined bandwidths.
 16. A system as recited inclaim 14, wherein said computer includes memory means for storing saidimages during their process.
 17. A system as recited in claim 14,wherein said computer includes at least one of a storing device, aninput device and an output device.
 18. The use of the system of claim14, for lead-coplanarity inspection.